Removal of silicon tetrafluoride from hydrocarbons



April 24, 1,951

J. D. GIBSON REMOVAL OF' SILICON TETRAFLUORIDE FROM HYDROCARBONS Filed April 22, 194e 2 Sheets-Sheet 1 ATTORNEYS Filed April 22, 1946 2 Sheets-Sheet 2 INVENTOR. J.D.G|BSON April 24, 1951 J. 5. GIBSON 2,550,343

REMOVAL lOF SILICON TETRAFLUORIDE FROM HYDROCARBONS BY /Wm ATTORNEYS Patented Apr. 24, 1951 STATES PATENT cfr/'Fica REMlovAL or s1Liggi)sfllliz'rRAFLUolimz4 James Gibsoml'artlesville, kla .,assignor to4 Phillps'letroleliin Company, a`v corporation fv ApplicationprilZZ; 1946; SerialfNo. 663,829,

This invention relates to the removal ofsilicon tetrafluoride from hydrocarbons.. In onepartic-y ular embodiment Vthis invention relates to the prevention of siliceousdeposits which may accumulate in condensers used in the fractiona-4 tion-of: hydrocarbons; ln, one particular aspect thiscinvention relates toA the removal of fluor-ine compoundssuchf `as hydrogen fluoride andsilicontetrailuoride. from a hydrocarbon stream: in which the uorine compounds? areil present as; impulitiesff'ormedlV in `a process for thev conversionv of hydrocarbons in'` the presencek of iluorine-con taining` catalysts;

In the manufacture of hydrocarbons-byyprocresses; inV` whichz fluorine-containing catalysts are used,..small,propontions of organic iiuorine-cm-A taining byeproductsfare formed. These processes may involve reactions such as polymerization, isomerizatiom dispro'portionation and alky-lation oftrelatively low-boiling, hydrocarbonsV to producel motor-fuels of high octane quality andare eiected in theipresence of catalystscomprisingioneor more: of such fluorine compoundsa's hydrofluoric acidi. boron trifl-uoride, or the like; Althoughthe exact nature or compositionlof theiforganicy `fluorineecontaining by-'products wh-ichamaybe formed: hasy not -been dellinitely"established, theyV are believed tol be" predominantly Aalkyl and/or anylwfluorides. .'Ilhesefluorides'are--noticompletelyfremovedaby Washing-Y the. hydrocarbonsfw-itn alkalirsolutionse.suchfrasfaqueous solutions ofT soul dium hydroxidessorV sodium vcarbonate;` The-fluo; rides-tend to decompose at=.elevatedtemperatures suchr as` those employed in fractional distillationof` thefhydrocarbons, thereby vforming :hyclrofluor-l icaacid, Which-.iscorrosiva especially in the pres-J' enceon moisture. Inl gases-,they may fthuscause' corrosion-fof handling equipment; l ini-liquid,- mo'- tor-fuel hydrocarbons;1 they are undesirable for reasonsthat areobvious. K Y

p discussed in4 i-E'rey Patent-2,347,9455w issued; Maly.v 2,1 1944:,A such organi-c fluorine compoundsmay:- b`e removed from hyglrocarbonA `materials containingthem by contacting. suchahydrocarf;

bonmaterial with any cnewof vafnumberfofsolid porous contact materials. Contact materialsn which have beenefound suitablelincludealumina:V gel,` activated alumina, dehydrated bauxite,` chromium:` oxide,lfmixtures of alumina andchromium oxide, chromium.. oresv comprising chromium. ox-` ide: and :ores of related materials suchLas those" containingezirconia, limestone, .magnesia and the like Such contact' materials appear to. adsorbl preferentially the. organic iluorine compounds- 1 although the vexact-1mechanismA involved-` -is- Ynot`- known aty presente Materials which contain.

' large: quantities of silicondioxide ory of: various` 2'. tain appreciable amountsA of silica or silicates; @ne such material which has found Wide come mercial use is hard granular bauxite.y Su'chfV bauxite has a variablen composition',. Wliich'niayY be exemplied by the following typical analysis; i-nfper` cent lbyvveig-ht:

Tha presence" of' silica is=undesirable becauseY it causesy the" formation of .silicon tetraluoride: Nevertheless, in practice bauxite containingfup to lfandeven'ZOper ce'ntof silica'has-been used; in: theab'sence` of any alternativeifreadilyavail# able andeconomical material;v Whenfthe bauxite hasT become partially: spent for? such*A use andoi'- when the hydrocarbon material. being. treated-f is passed i throu'ghf the mass of" con'tactagent".l ati-ai righ flow rate, ithas been foundr thatsilicon tetra-f iluoride is present in the eiiluent; also, some Water; which appears to berform'edY by reaction' of-'the fluor-ine;v compounds With the l bauxitep isf'presentin the eiiluents. That is, after conversion-iofftheA hydrocarbons, either in the liquid or vapor phase, in the presenceotilumine-containing catalysts, such as hydrogen fluoride, boron trifluoride and the complexes of the same With other compounds, silicon tetraluoride is formed When the hydrocarbon conversionieiiluent is contacted with contact-materialscontaining minor proportions of silica. Thus, thel conversion effluent after removal of the organic uorine compounds comprises the conversion product;r various lower-boiling byproducts formediduring conversion, and the relatively low-boiling;1 siliccnhtetrafluoridef and Water.

It is necessarlyginimost cases, to remove the organic luorine compoundsbyrcontactinga the hydrocarbqn effluentwith, a `suitable contact material; but as aresult'ofthis treatmentsilicoh'ttiai fluoride andfyater are liberated`th`react of: hydrogen-iluorid o'rfthe organic fliorlrle corn'- poundsqwithsilica presentla's an'` iirpuriffyv ififtle contact material".` Typical'epliatio'nsoqreactiors'V Which-mayoccur in the treatmentlof"the'eilleit with f bauxite are: i

Although bauxite hasybeerifrefrredlto 4{.inp'ar 3 ticular, any type of contact material suitable for the sorption of organic I'luorine compounds in which minor proportions of silica are present are within the scope of this invention.

After being formed, the silicon tetrafiuoride and the water are conveyed along with the hydrocarbon efuent from the contact material to subsequent treating equipment, which is usually fractionating equipment, for the separation and purification ofthe conversion product. The silicon tetrafluoride and water accumulate in the overhead fractions from the various fractionators, since they comprise some of the low-boiling components of the hydrocarbon eiiluent. In consequence, trouble is experienced in the subsequent treating equipment as a result of the silicon tetraiiuoride reacting with water to form -various solid siliceous deposits. When the effluent of the bauxite treatingstep just discussed is in the liquid phase, and the proportions of silicon tetrafluoride and water are so small that these materials are completely dissolved, relatively little or only minor trouble may be experienced, if any. However, when much of the heavier hydrocarbon materials have been removed by fractional distilmixture,l the silicon tetrauoride reacts with the f;

water, forming siliceous deposits that accumulate, thereby partially or completely plugging equipment and necessitating an expensive shutdown and interruption of production in order to remove the siliceous deposits. Sometimes the deposits form in the condenser of the rst fractionator, such as the deisobutanizer; sometimes the deposits may not form until the eiuent has reached the condenser of the second fractionator, such as a depropanizer; sometimes the deposits form in the condensers of all the fractionators.

. The following equations are illustrative of reactions involved in the hydrolysis of silicon tetrauoride:

sirl m2o Hisicl 4HF Orthosilicic acid H2Si03 -I- H2O Metasilicic acid The formation of orthosilicic acid results in a geltype deposit which tends to accumulate and plug the condenser tubing and reflux pipes and valves. Under appropriate conditions orthosilicic acid decomposes to metasilicic acid or silicon dioxide, Which are solid precipitates and which also obstruct the passage of hydrocarbons through the condensers and tubings of the fractionating equipment.

The deposits appear to vary with the proportions of water and silicon tetrauoride in the hydrocarbon stream; and these proportions in turn vary with such Vfactors as the degree of spending of the bauxite. l

The amount of organic fluorine present in the charge to the treating step for the removal of fluorine compounds generally is not more than about 0.1 per cent by weight and often is not more than 0.001 to 0.05 per cent by weight. Most of this organic uorine is retained by the treating agent, and the silicon tetrafiuoride in the eiiluent from this treating step generally is less than about 0.01 per cent by weight, and often is less than 0.005 per cent by weight. Nevertheless, in commercial plants, wherein several hundred barrels of hydrocarbons are treated per day and the silicon tetraiiuoride reacts with water to form solid siliceous deposits in certain specific locations, suoh as the condenser and accumulator of a deisobutanizer or a depropanizer, the amount of solid siliceous material accumulated over a period of a few weeks or a few months amounts to a very substantial amount.

The object of this invention is to remove organically combined iuorine from a hydrocarbon iiuid containing the same.

An object of the present invention is to provide a process for preventing the formation of siliceous deposits in condensers of fractionating equipment used for the separation of the product of a hydrocarbon conversion process.

It is also an object to prevent the plugging of condensers and tubing wherein siliceous deposits are accumulated as the result of the presence of silicon tetraiiuoride in the condensate.

Another object is to prevent the corrosion of fractionating equipment caused by the liberation of acids in the condensers and tubing of the fractionating equipment.

A still further object is to remove inorganic fluorine compounds from a hydrocarbon conversion effluent from an alkylation process using a iiuorine-containing alkylation catalyst.

A further object is to produce a high quality motor fuel substantially free from undesirable fluorine impurities.

Other objects and advantages will appear obvious to those skilled in the art from the accompanying disclosure and description.

According to this invention, the formation of siliceous deposits in condensers, accumulators, reflux pipes, etc. of fractionating equipment of hydrocarbon conversion processes using a fluorine-containing catalyst is prevented or minimized by removing silicon tetrafluoride from the hydrocarbon stream passing to the aforesaid fractionating equipment. Unexpectedly, it has been found that fluorine compounds, including silicon tetrafluoride, are removed from hydrocarbon materials containing the same by contacting the hydrocarbon materials with an oxide of iron. In the application of this invention to an alkylation process using the iiuorine-containing catalyst, the hydrocarbon eiiluent from the treater for the removal of the organic uorine compounds is contacted with an oxide of iron at a suitable location at or between the treater and the place where siliceous deposits have been found to occur.

Of the various oxides of iron, ferric oxide is preferred; however, ferrous oxide and mixtures of the various iron oxides may be used as the silicon tetrafluoride-removing material without departing from the scope of this invention. Ferrie oxide is readily available as a natural material in the form of hematite and limcnite and as a Waste material in the form of iron rust and cinders from pyrte burners. Ferrie oxide from such sources is relatively inexpensive. When the ferric oxide contains moisture or water of hydration'it is preferably dehydrated before use in 51 order to render ythe ferrie oxide contact material substantially free from moisture.

The hydrocarbon material to be freed of the silicon tetrafluoride and any other fluorine compound is passed over the iron oxide in the closed chamber at a space velocity of about l to about volumes of liquid per volume of iron oxide per hour and at a temperaturebetween about and about 550 F. Preferably the pressure during the contact process is maintained suiciently high to ensure contact in the liquid phase since,` as a general rule when operating in the liquid phase, the temperature of the hydrocarbon stream will be lower than when operating in the vapor phase. A lower temperature of contact enables a higher efciency of silicon tetraiiuoride removal by the iron oxide. It is preferred to maintain the temperature of the hydrocarbon stream contacting theiron oxide below about 250 F. to obtain optimum removal of silicon tetrafluoride. Although liquid phase operation of the contact treatment with iron oxide is preferable, vapor phase operationl of the contact operation is within the scope of this. invention.

Normally, in the treatment of hydrocarbon conversion eilluents with bauxite containing a minor proportion of silica to remove the undesired organic uorine compounds, besides silicon tetrafluoride being formed by the contact with the bauxite some hydrogen uoride is also formed as previously indicated. Thus, the effluent stream from the bauxite contact operation may contain not only silicon tetraluoride but relatively small amounts of unremoved organically combined iiuorine and hydrogen fluoride as impurities. During contact with the iron oxide, not only is the silicon tetrafluoride removed but also these other impurities, such as organically combined fluorine and hydrogen fluoride.

As indicated by the specimenanalysis previously given, many bauxites contain iron oxide. The iron oxide content is sometimes considerably higher than that shown. Unfortunately, however, this iron oxide does not effectively remove the silicon tetrafluoride formedduring contact with organic fluorine-containing materials. Although the reason for this nonremoval is not completely understood, it is possible that the iron oxide may exist-in solidl solution with thev bauxite and thus may be present in such a degree of dilution as to be ineffective in removing silicon tetrafiuoride. Regardless of any postulated explanation, however, it has been experimentally demonstrated that, even when relatively highly ferriferous bauxite is used to remove organic iluorine compounds from hydrocarbon effluents from iluoride-catalyzed conversions, the previously described operational diillculties due to silicon uoride formation are observed.

In a preferred embodiment of the present invention an organic mixture containing organic fluorine compounds is passed in either the liquid or vapor phase to a treating Zone lilled with a powdered or granular deiluorination material and an oxide of iron. The contents of the treating Zone are usually arranged in such a manner that the contact material for removal of organic uorine compounds and the iron oxide are in alternate layers. By such an arrangement the first layer of contact material removes the organically combined fluorine with the liberation of silicon tetrafluoride and the subsequent layer of iron oxide removes thev silicon tetrauoride, etc., 'and the process is repeated in the nextsuccessive` layers;

which permits. the ready passage of gases or liquids and serves to expose the iron oxide to the fluid stream. Replaceable trays-separately containing contact material and iron oxide may be placed in the contact chamber in 4alternate layers. When the iron oxide or the contact material "becomes spent, the tray may be removed and either a new tray of fresh material inserted therein or the material in the tray may bere-A vivied. Preferablythe alternate layers of or`" ganic fluorine-removing material and iron oxide in a treating column are supported in such manner that free space exists between the supported layers. This arrangement is especially desirable since the tendency for channeling of the liquid hydrocarb-on stream through the con-- tact material is minimized. Thev number of' layers of the zone which will be suitable for re moval of the organic fiuorine compound dependsA upon several factors such as the type of organic'- fluorine removing material, the conditions of' temperature and pressure and Ythe depth of the contact bed; such conditions and the number: of successive layers or zones may be easily determined by trial; In general, layers from about 3 to about 6 inches in depth of organic iluorineremoving material and of iron oxide,l respectively, will be suiiicient when a total of about l0 to about 25 layers are used in the treating zone.

Another embodiment, which may also be practiced, is the arrangement of the organic iluorine-removing material and the iron oxide in successive zones rather than in a single' zone;

thus the contact material will be maintained in one separate zone or column and the iron oxide will be maintained in a second and successive zone or column.

In still another embodiment of the present invention the organic fluorine-removing material and iron oxide may be admixed in a treating zone in a substantially uniform manner and the organic mixture contacted with the uniform mixture of organic fluorine-removing materialy after the organic luorine-removing step or onf the overhead from the various fractionators oron the feed to the various iractionators. When a separate silicon tetrafluoride removing step is used, iron oxide chambers are placed on the iso-- butanizer overhead, or on the feed to the de*- propanizer, or even on the depropanizer overhead. Any one of these placesl of treatment alone may be suiiicient in order to prevent the precipitation of siliceous deposits, but in some cases it may be necessary to place treaters as suggested in all the locations. In many instances it maybe necessary or desirable vto remove organically combined fluorinefrom thev bottom fraction from the deisobutanizer. Very often, therefore, a treating chamber containing.

organically combined. fluorine-removing material and iron oxide is placed on the `bottom discharge line from thev deisobutanizer..

Obviously. Various locations may become; apa@ The iron oxide may be i'ixed with a suitable supporting or carrier material,

.parent to those skilled in thel art for'placing either the combination organic fluorine and the silicon tetrafluoride-removing step orsolely the ysiliconYtetrafluoride-removing step. The removal of organically combined fluorine may be conducted under similar operating conditions as those for the removal of silicon tetrailuoride; thus where the two contact materials are .mixed similar conditions may be used. Where the organic fiuorine-removing material and the iron oxiderare in separate zones or columns somewhat different conditions of temperature and pressure etc. may be used for each column. However, due to economic considerations in most instances it is desirable to maintain substantially the same conditions in both the organic fluorine-removal zone and in the silicon tetrailuoride-removal zone.

' Revivication of the organic iluorine-removing material and the iron oxide is accomplished under approximately the same conditions. The contact material and the iron oxide are revivied by passing superheated steam at a temperature from about 400 to about 860 F., preferably from about 500 to about 606 F. and at approximately atmospheric pressure through or in Contact with the various contact materials. For economic reasons, the spent contact material and iron oxide are usually disposed of as waste and fresh material is used in their place without a revivication process.

Although the iron oxide contact operation can be applied with advantage in many modiiicaticns to the removal of silicon tetraluoride and in some cases to the removal of organically combined uorine and hydrogen fluoride, particular benefits of it have been realized in connection with the removal of silicon tetraiiuoride from a conversion eiiluent from the alkylation of an alkylatable hydrocarbon with an olefin in the presence of a fuorine-containing alkylation catalyst.

It is believed that the principles of this invention may be adequately illustrated by the discussion of a specific embodiment in connection with the accompanying drawings which form a part of this application and which illustrate diagrammatically an arrangement of apparatus suitable for practicing this invention in connection with an alkylation process.

Figure 1 illustrates an arrangement of apparatus for an alkylation process in which an embodiment of this invention may be practiced.

Figure 2 diagrammatically illustrates the arrangement of organic fluorine-removing material and iron oxide in contact zone Il of Figure 1.

Figure 3 also illustrates another embodiment of the present invention in which the contact material and iron oxide are arranged in successive and separate zones for the removal of organically combined iluorine and silicon tetrafluoride from the hydrocarbon stream of line I5 of Figure 1. Referring to Figure l oi the drawings, a hydrocarbon feed comprising a mixture of lowboiling isoparafns and low-boiling olens enters reactor 6 through line 5. For example, typical low-boiling isoparains comprise isobutane, isopentane, etc., and typical low-boiling olens comprise propylene, butenes, amylenes and hexenes. Any desired type of reaction chamber or series of chambers may be employed without departing from the scope of this invention. Hydrogen iluoride catalyst is introduced through lines 4 and 44 to reactor 6. Alkylation of hy-l drocarbons is accomplished under known conditions of pressure, temperature, and residence time in reactor 6. Preferably, the reaction is maintained at a temperature between about 50 and 150 F. land under sufficient pressure to maintain the kreactants in the liquid phase. The mol ratio of isoparain to olen should be relatively high in the reaction zone itself, usually as high as :1 or more. A conversion ellluent from reaction zone 6 passes through line 1 into a separator 8 in which the eiiluent is separated into two liquid phases, namely, a hydrocarbonrich phase and a heavier hydrogen fluoride-rich phase. The liquid hydrogen uoride-rich phase is withdrawn from separator 8 through line 9 for purication (not shown) if desired, or the hydrogen fluoride-rich phase is recycled as a catalyst through lines II and 44 to reactor G. The liquid hydrocarbon-rich phase containing some dissolved hydrogen fluoride and organically combined .uorine passes from separator 8 to an azeotrope tower I3 via line I2. Separation of a practically azeotropic minimum-boiling mixture of hydrocarbons and hydrogen uoride is effected in tower I3 by distillation. The azeotropic mixture containing relatively low-boiling hydrocarbons and hydrogen fluoride passes as a vapor from tower I3 through line I4 and condenser I5 to separator 8. A liquid hydrocarbon streanrrsubstantially free from hydrogen fluoride but containing organic iiuorine compounds formed during the alkylation reaction, passes from the bottom of tower I3 through line I6 to a bauxite treater I l. These organic uorine compounds, which are formed as by-products or" the hydrocarbon conversion, are removed by treatment with a suitable contact material, such as dehydrated bauxite or alumina, in treater Il. When siliceous material, such as silica or various natural silicates, is present in the contact material, silicon tetrauoride is formed and appears in the eiiluent from treater Il. The presence of silicon tetrafluoride in the eiiiuent from treater I l is especially evident when the contact material is partially spent and/or when an economically desirable high flow rate is used.

In order to prevent the presence of silicon tetrailuoride in the eilluent from treater I'I, treater Il comprises, according to an embodiment of this invention, successive layers of contact material, such as dehydrated bauxite, and ironoxide or comprises a uniform mixture of a contact material and iron oxide. An arrange- ,Xment of iron oxide and bauxite is shown in Figure 2 of the drawing and will be discussed more fully hereinafter. Another arrangement of the bauxite and iron oxide for treatment of the eiiiuent stream at this point is shown in Figure 3 of the drawing and will also be discussed more fully hereinafter. In many cases it is sufficient or even desirable to remove the silicon tetraiiuoride from the feed to the various fractionating units or from the overhead from the various fractionating units; therefore, treater I'I may contain only bauxite for the removal of organic fluorine compounds and not iron oxide. The removal of the silicon tetraiiuoride from the hydrocarbon stream at other points in the alkylation process will be discussed hereinafter.

The eiiiuent from bauxite treater I'I is removed therefrom through line deisobutanizer 20. A portion of the effluent from-` I8 and passed to avapors pass to accumulator 39.

treater l1 may ,be `recycled `to treater :through line lo, if desired.

vNorm-al b-uta-ne and heavier hydrocarbons are :separated from isobutane and lighter hydrocarbons in deisobutaniner 20, which is a fractionating column complete `with a .condenser 2li and an accumulator 25. `Normal butano and heavier hydrocarbons are Withdrawn from deisobutanizer 20 via line 2l and, if this stream .contains organically combined iifuorine, 'it is passed through another bauxite treater 26 to remove the organically .combined iluorine. As .inv bauxite treater l'i if .silicon tetra-Fluoride is formed during the treatment, the silicon tetraiiuoride may be removed from the resulting stream by `:charging 'bauxite treater 28 with sufcient iron oxide to remove the silicon tetrailuoride. A butane and heavier hydrocarbon stream :substantially free from organically combined; fluorine and silice-n tetrafluoride is conveyed through line 2l to subsequent lf ractionators and process equipment (not shown) for separation and .recovery of butano vand an alkylation product; also a portion of the butano and heavier hydrocarbon stream Afrom deisobutanizer 'Z'Q'may be recycled to reactor .6 by `means not shown.

The overhead product ffrom deisobutanizer 2li comprising isobutane and lighter hydrocarbons passes there.from through line 2,2 and a condenser -24 into accumulator 21o. Vaporous hydrocarbons are condensed in ,condenser 2t and are accumulated as a liquid in accumulator 26. A portion `of the hydrocarbon Vliquid ,from accumulator 2 5 lis `returned through line .21 to deiscbutanizer 2e as .a liquid redux therefor.. If conditions of temperature and pressure within accumulator 2i5 and condenser 2d are approprialle, particularlyfi-i thexsolubility of the water in the ,hydrocarbon is decreased sufliciently to form a separateliq-uid water phase, .and `it v the silicon tetrafluoride Ihas `not been previously removed, siliceous deposits are vformed and accumulate in condenser 2li and accumulator 2t. Sometimes the siliceous deposits even accumulate in line :2l and subsequent 4fractionating equipment through which the hydrocarbon stream is passed. In order to prevent the formation of such siliceous deposits according to this invention whenall the silicon tetrafluoride has not been previously removed, a treater .23 containing an oxide .of iron is inserted in line 22, preferably before condenser 24, .as shown, although the particular location .of Vtreater 2.3 is not considered critical to the operation of lthe invention as long as the silicon tetrailuoride present in the str-earn at this point is removed prior to hydrolysis thereof..

.At least a portion, and .ordinarily all, of the overhead product from .the deisobutan-izer Eil passes 4from accumulator 26 into a depropanizer 3,2 `via line 29 for the separation Aof isobutane` from vpropane and lighter hydrocarbons. Iso? butano, which is incidentally dried as a result of the depropanization, is removed from thebo't'- tom of thedepropanizer 32 through line 35 or is recycledby lines .d3 andr@ to reactor e as the circumstances'magy require. The overhead iraction comprising propane and lighter hydrocarbons from depropanizer 32 passes to condenser 33 through line 34, ,and from condenser 3Bv condensed hydrocarbons and uncondensed Some of the liqudoondensate is returned to v`depronani.zer i2 through line Al as reflux therefor. Propane and other light hydrocarbons are withdrawn from accumulator 3,9 through line 42,

If desi-red, part or -even all of :the overhead product from deisobutanizer 2,0 may be recycled to reactor 6, as by passing from accumulator 26 through line 44, particularly When the proportion of propane and lighter .hydrocarbons 'is relatively small; in such case a drier (not shown) may be provi-ded -11o-remove water .from this recycle product.

Frequently in the operation of .such alkylation processes the accumulation .of siliceous deposits in the condenseror .tubing of the depropanjizing equipment becomes so serious as to curtail thecapaci-ty thereof. In turn, because of vthe resulting ineiiicient removal of .propane and lighter gases, continuation .of :the operation necessitates resorting to .increased venting oi such gases through :line l0 from separatori! in order to maintain a pressure Within the operating limit. The extra venting adversely Aaiects the alkylation by increased hydrogen vfluoride consumption and the loss of valuable isobutane and normal butano. The most serious accumulation and formation of .siliceous deposits is ordinarily observedV in the depropanizing equipment, wherein the conditions of temperature and pressure and Water concentration are more citen such as to form a separate Water phase in the condenser, accumulator and .even on somev of the `fractionating plates Yof the depropanizing column 32. 'Therefore `according to a speciic embodiment of :this invention, when the hydro` carbon stream at this point contains silicon tetraiiuoride, a treater 131 V.containingiron oxide is inserted in line .29 as shown. "In most cases treater 3l will remove enough of the silicon tetrailuoride from the 'hydrocarbon stream to prevent formation of siliceous deposits .in any of the accessory equipment of depropanizer '32.; however in some cases it may be desirable or necessary to insert an additional treater 3'! in overhead line 35i of depropanizer T32. When it is desired, therefore, the overhead line 3i passes through a treater 3l containing an oxide ofr iron and the effluent from the treater '31 passes to accumulator 39. Treaters 23,31 and .3l may be used alone or in combination with each other Without departing from the scope of this invention. When a treater is not being used the hydrocarbon stream may .by-pass the treater through lines 25, 33 and ,36.

'In practice siliceous deposits often form in the fractionating tower itself. VOften this 'formation is evident by the presence of the siliceous depositson the top fractionating plate and byY deposits in' decreasing amounts on succeeding plates down the tower. By a substantially complete removalof silicon tetraluoride from the hydrocarbon' stream entering the tower the hydrolysis ofl silicon tetrafluoride is prevented and the accumulation of siliceous deposits in the towereliminated. Complete removal of silicon tetrafluoride also prevents the carry-over and formation of further deposits in subsequent equipment.

In the regeneration of bauxite-treater H with hot gases, such as steam, the gases may be introduced into treater |11 through lines 46 and withdrawn through line 41. Bauxite treater l1 may represent a group of parallel treaters so that one treater may be on regeneration While the other treater may beonprocess flow in order to achieve a continuous process. l

Figure 2, diagrammatically representing apparatus for an embodiment Oftreater I1, shows alternate layers .of organic .fluorine-removing material and iron oxide. VThe hydrocarbon eiliuenty from azeotrope tower I3 of Figure 1 enters treating unit II through line I6 and is removed therefrom through line I8. A portion of the resulting effluent may be recycled through treater II through line I9. Numeral 53 of Figure 2 designates successive layers of bauxite or other o1'- ganic iiuorine-removing materials and numeral 54 designates successive layers of iron oxide for removing silicon tetrauoride and any hydrogen iiuoride present.

Figure 3 diagrammatically represents another arrangement of apparatus for treating unit I'I in which the organic iiuorine-removing material and iron oxide are contained in separate columns. The hydrocarbon eluent from azeotrope tower I3 of Figure 1 passes through line I@ into column 'II which contains organic iiuorine-removing material, such as bauxite, designated by numeral l2. The treated hydrocarbon eiuentis withdrawn from column 'II through line 'I3 and is vintroduced into a second column 'I4 which contains iron oxide designated by numeral 16. The iron oxide removes silicon tetrafluoride formed in column 1I. The eiiiuent from column Id is removed by line 'II and a portion thereof may be.

recycled to column 'II Vthrough line T8, if desired. Eiluent from column I is passed to column 'I9 which also contains an organic fluorine-removing material. The resulting eiiiuent from column 'I9 is removed therefrom through line SI. This eiliuent from column 'I9 is passed to column 32 which contains iron oxide for the removal of silicon tetrafluoride formed in column 19. The eluent from column 82 is removed by line I8 and a portion thereof may be recycled to column 'I9 through line 83. The total effluent from the treating step is removed through line I8 and passed to deisobutanizer 29 of Figure 1. Any number of successive columns of organic uorine-removing material` and iron oxide may be used; the number of columns will depend upon the requirements necessary for removing the desired amount of organic iiuorine compounds from the hydrocarbon eliuent. A portion of the resulting eiiiuent from the treating step of Figure 3 may be recycled from line I8 through I9 to line I6.

The following examples illustrate the operability of the present invention and are not considered unnecessarily limiting to the invention.

Example I Normal butane containing 0.059 weight per cent silicon tetraiiuoride was passed through a chamber containing rusty iron lings at about 180 F. The space velocity of the normal butane stream Y condition and the results of the treatment were as follows:

Space Velocity, Liquid Vol. per Vol. of Catalyst per hour Silicon tet- .railuoride m effluent, wt. per cent Silicon Tetraiiuoride removed,

per cent Eample II free liquid kettle fraction is passed through a series of two chambers, the rst of which contains dehydrated bauxite and the second of which contains dehydrated limonite. The temperature and the pressure in the chambers were F. and about 200 pounds per square inch gage, respectively, and the overall space velocity through the two chambers is about 2 volumes of liquid hydrocarbons per Volume of bauxite and limonite per hour. Substantially complete removal of organically combined fluorine occurs in the first chamber and substantially complete removal of silicon tetrafluoride occurs in the second chamber.

The present invention may be applied in many processes in which silicon tetrauoride is present and in which it hydrolyzes owing to the presence of water to form siliceous deposits. Although the invention has been applied specically to hydrocarbon conversion processes, the present invention is not limited or restricted to such processes in its broadest aspects; it is also not restricted in all instances to the source of water and the silicon tetrafluoride or to the location of the particular siliceous deposits.

Having described the preferred form of the invention and having pointed out the principal considerations to be observed in its operation, and in operating of equivalent systems, it is obvious that various other changes can be made Without departing from the scope of the invention.

Having described my invention, I claim:

1. In a process involving the conversion of hydrocarbons in the presence of a fluorin'e-containing catalyst in which a liquid hydrocarbon conversion eiuent is contacted with an organic nuorine-removing material containing a minor proportion of silica and thereby is contaminatedwith water and with a minor amount of silicontetrauoride of less than 0.1 per cent by weight of said eiiiuent, and in Which components of a resulting eiiiuent are separated by fractional distillation under conditions such that water and silicon tetraiiuoride are concentrated and silicon tetrafluoride is hydrolyzed to form siliceous deposits by the condensation of a relatively low-boiling fraction from said fractional distillation, the method for preventing the formation of Such siliceous deposits which comprises contacting said low-boiling fraction from which said deposits separate with an oxide of iron under conditions such that silicon tetrafluoride is removed by said iron oxide from said low-boiling fraction prior to the condensation thereof.

2. In a process involving the conversion of hydrocarbons in the presence of a iiuorine-containing catalyst in which a liquid hydrocarbon conversion effluent containing organic uorine compound is contacted with an organic uorine-removing material containing minor proportions of silica under conditions such that the resulting effluent is contaminated with Water which is present in an Aamount less than about 1 per cent by Weight, with silicon tetrauoride which is present in an amount less than about 0.1 per cent by Weight and with a minor amount of unremoved organic iiuorine compounds, the method for removing said contaminating silicon tetrafluoride and said unremoved organic fluorine compounds from the resulting eiuent which comprises contacting said resulting eiiiuent with a body of fluo-- rine removing material comprising an organic uorine-removing material and an oxide of iron at a temperature between about 50 and about volumes of liquid per volume of iron oxide per hour under sufficient pressure to maintain the eluent in the liquid phase and removing said hydrocarbon conversion effluent free of said organic luorine compounds and of said silicon tetraluoride.

3. The process of claim 2 in which said oxide of iron is ferric oxide.

4. The process of claim 2 in which said oxide of iron is ferrous oxide.

5. The process of claim 2 in which said oxide of iron is a mixture of ferrie oxide and ferrous oxide.

6. In a process for the alkylation of a low-boiling isoparafn with a low-boiling olefin in the presence of a hydrofluoric acid alkylation catalyst wherein organic fluorine compounds are formed as lay-products of said alkylation and contaminate a hydrocarbon alkylation ellluent, the method for removing the organic fluorine compounds which comprises separating said hydrocarbon allcylation effluent into a liquid hydrocarbon-rich phase and a liquid hydrofluoric acid-rich phase, passing said hydrocarbon-rich phase containing dissolved hydrouoric acid and a minor proportion Vof organic uorine compounds to a fractional distillation, separating in said distillation a relatively low-boiling fraction comprising substantially all of the dissolved hydrouoric acid and a relatively high-boiling fraction containing organic rluorine compounds, passing said highboiling fraction through a treating Zone for the removal of organic fluorine compounds from said high-boiling fraction, said treating zone comprising alternate bodies of silica-contaminated ,organic fluorine-removing material and iron oxide arranged in such a manner that the highboiling fraction passing therethrough successive- 1y contacts said alternate bodies whereby the resulting silicon tetrafluoride formed in an amount equal to about 0.1 weight per cent upon contact with said organic fluorine-removing material is removed by said iron oxide, and removing from said treating zone a hydrocarbon effluent substantially free from luorine compounds.

7. In a process involving the alkylation of isobutane with an olefin in the presence of a hydro- 14 uoric acid alkylation catalyst in which a liquid hydrocarbon conversion eiliuent is contacted with bauxite containing a :minor proportion of silica to remove organic iiuorine compounds formed during said conversion and thereby is contaminated with water and with silicon tetraiiuoride which is present in an amount less than 0.1 per cent by Weight, and in which normal butane and heavier hydrocarbons are separated from isobutane and lighter hydrocarbons of a resulting hydrocarbon eluent in a rst fractional distillation and isobutane is separated from propane and lighter hydrocarbons in a second fractional distillation under conditions such that said water is concentrated in the lighter fractions and said silicon tetrafluoride is hydrolyzed thereby to form siliceous deposits during condensation of at least one of the overhead fractions of said distillations, the method for preventing formation of such siliceous deposits which comprises contacting at least a portion of said overhead fractions from each of said distillations from which such deposits separate with an oxide of iron under conditions such that silicon tetrauoride is removed by said iron oxide therefrom prior to the condensation of said fractions.

JAMES D. GIBSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES V PATENTS Number Name Date 1,293,703 Catlin Feb. 11, 1919 2,347,945 Frey May 2, 1944 2,403,714 Frey July 9, 1946 2,409,372 Matuszak Oct. 15, 1946Y 2,413,868 Frey Jan. 7, 1947 2,430,453 Cole Nov, 11, 1947 2,430,460 Frey Nov. 11, 1947 OTHER REFERENCES Mellor: A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 6, page 939.

Martin: Anales fis. y quim. (Madrid), 41, 1303- 16 (1945), cited in Chem. Abstracts, vol. 41, page 4404i. 

1. IN A PROCESS INVOLVING THE CONVERSION OF HYDROCARBONS IN THE PRESENCE OF A FLUORINE-CONTAINING CATALYST IN WHICH A LIQUID HYDROCARBON CONVERSION EFFLUENT IS CONTACTED WITH AN ORGANIC FLUORINE-REMOVING MATERIAL CONTAINING A MINOR PROPORTION OF SILICA AND THEREBY IS CONTAMINATED WITH WATER AND WITH A MINOR AMOUNT OF SILICON TETRAFLUORIDE OF LESS THAN 0.1 PER CENT BY WEIGHT OF SAID EFFLUENT, AND IN WHICH COMPONENTS OF A RESULTING EFFLUENT ARE SEPARATED BY FRACTIONAL DISTILLATION UNDER CONDITIONS SUCH THAT WATER AND SILICON TETRAFLUORIDE ARE CONCENTRATED AND SILICON TETRAFLUORIDE IS HYDROLYZED TO FORM SILICEOUS DEPOSITS BY THE CONDENSATION OF A RELATIVELY LOW-BOILING FRACTION FROM SAID FRACTIONAL DISTILLATION, THE METHOD FOR PREVENTING THE FORMATION SO SUCH SILICEOUS DEPOSITS WHICH COMPRISES CONTACTING SIAD LOW-BOILING FRACTION FROM WHICH SAID DEPOSITS SEPARATE WITH AN OXIDE OF IRON UNDER CONDITIONS SUCH THAT SILICON TETRAFLUORIDE IS REMOVED BY SAID IRON OXIDE FROM SAID LOW-BOILING FRACTION PRIOR TO THE CONDENSATION THEREOF. 